This invention relates to compositions and methods for household laundry operations for combined washing and bleaching of cotton fabrics. Removal of stains from cotton fabrics is thereby accomplished.
Certain published references have disclosed the use of zinc phthalocyanine sulfonates as bleach photoactivators in detergent compositions: U.S. Pat. No. 3,916,652 issued to Speakman on November 4, 1975, hereinafter referred to as Speakman I; U.S. Pat. 3,927,967 issued to Speakman on December 23, 1975, hereinafter referred to as Speakman II; Japanese OPI 50-113,479 laid open to public inspection on Sept. 5, 1975, invented by Holcombe and Schultz, corresponding to USSN 419,320 filed Nov. 27, 1973 and to Canadian application 214,688 filed Nov. 26, 1974; and Japanese OPI 51-135,883, laid open to public inspection on November 25, 1976, invented by Wiers, corresponding to USSN 564,587 filed Apr. 3, 1975 and to Canadian Application No. 248,598 filed Mar. 23, 1976.
Speakman II discloses a number of bleach photoactivators in detergent compositions which contain an alkaline builder salt and preferably a surfactant and a peroxyhydrate. Fabrics treated with these compositions in the presence of visible light and atmospheric oxygen are subjected to a combined washing and bleaching process for household laundry. A preferred photoactivator is zinc phthalocyanine sulfonate used at concentrations of 0.025 to 1.25% by weight of the product composition. Speakman's preferred washing conditions are photoactivator concentrations of 1-150 ppm., temperatures of 80.degree.-160.degree. F., and times of 15 minutes to 5 hours. Speakman specifies exposure of the aqueous laundry baths to visible light, whether outdoors or indoors, whether agitated (e.g. during washing), or unagitated (e.g. during soaking).
Speakman I teaches the practice of the Speakman II process in a washing machine provided with a source of visible light.
The intrinsic color of zinc phthalocyanine sulfonate is blue-green, and when it is present on fabric surfaces they take on this undesirable coloration. This occurs in the absence of light, because in that circumstance the bleach photoactivation process which decolorizes zinc phthalocyanine sulfonate does not take place. Holcombe and Schultz were concerned about this problem, and disclosed certain preferred mixtures of trisulfonated and tetrasulfonated species of zinc phthalocyanine which produced minimum levels of fabric discoloration at equal levels of bleaching. The most highly preferred photoactivator contained no unsulfonated, monosulfonated, or disulfonated zinc phthalocyanine; 6-16 parts trisulfonated; and the balance tetrasulfonated; where the specified parts are determined by an "RDV" method explained in the specification. The washing conditions of Holcombe and Schultz were similar to those of Speakman II, including the specified levels of 0.025-1.25 wt.% photoactivator usage on a product composition basis, except that photoactivator concentrations as low as 0.25 ppm in the laundry baths were disclosed. Certain examples concerned indoor washing of fabrics followed by exposure to the sun for bleaching, as by laying them flat on the ground, especially without rinsing, or by suspending them from an outdoor clothesline.
Wiers was concerned with zinc phthalocyanine tri- and tetra-sulfonates as bleach photoactivators in unbuilt liquid detergent compositions.
Although the blue-green discoloration problem may have been ameliorated by Holcombe and Schultz, it was by no means solved. When their specified levels of zinc phthalocyanine sulfonate are used in practical detergent compositions, effective bleaching occurs when these compositions are used in a washing process of relatively short duration, e.g. 10 to 30 minutes, but blue-green staining occurs when the same compositions are used in a soaking process that may last from one to as much as eighteen hours. Since the detergent manufacturer has no control over how its customers use any given product, and since soaking is a common practice, this is a serious disadvantage. It has now been found that the use of substantially lower amounts of photoactivator give effective photobleaching when used in the laundry soak and do not cause appreciable discoloration. When used in the wash, little bleaching takes place, but no disadvantages occur either. The result is that a manufacturer can deliver to the consumer a product which, when used in the wash, will perform like any other good detergent and, when used in the soak, will deliver bleaching performance as well.
This not only solves the discoloration problem; it also reduces cost by a significant amount, thereby making such a photoactivator-containing product more attractive to manufacturer and consumer alike.
It has also been discovered unexpectedly that the process of soaking need not involve exposure to light; hence it may be carried out for example in a closed washing machine, or in a dark room overnight. This is believed to be because the photoactivator adsorbs on the fabric in a kinetically slow process over the entire soaking period; little desorbs during rinsing because of the slow kinetics; and the remainder is present on the surface of the fabrics where it can effectively participate in a photobleaching process that takes place in the presence of visible light during drying. The presence of photoactivator on the fabrics during drying under visible light is shown to provide a stain removal benefit and may also provide a sanitizing benefit to the fabrics.